net: wireless: bcmdhd_xxx: fix overrun in wl_run_escan

prevent buffer overrun case where WLC_GET_VALID_CHANNELS IOCTL
 overriden by attacker and its return manipulated.

Signed-off-by: Insun Song <insun.song@broadcom.com>
Change-Id: Ifbbaa3c2bdfd9bea7533d605303f18e17c8d85cc
Bug: 34197514
CVE-2017-0568
Signed-off-by: Kevin F. Haggerty <haggertk@lineageos.org>